Inductive repulsion-type magnetically levitated railways in general are well known in the art. An example of such a railway, particularly the levitation, propulsion and guidance mechanism thereof, will now be described with reference to FIGS. 1 through 4.
Superconducting coils 1, 1' are vertically mounted on both sides of a truck 4 of a vehicle VH. Conductor coils 2, 2' which make use of both propulsive and guiding forces for both guidance and propulsion of the vehicle are arranged vertically and continuously at predetermined intervals in the direction of travel of the vehicle along both inner side walls of a track bed 9 having a U-shaped cross section. These coils 2, 2' are so disposed as to be capable of electromagnetically coupling with the superconducting coils 1, 1' mounted on the truck 4. Loop-shaped conductor coils 3, 3' for levitation of the vehicle are arranged horizontally on the bottom surface of the track bed 9 and extend continuously in the direction of travel of the vehicle. The arrangement of the coils is as illustrated in FIG. 2. A levitating force is applied to the vehicle VH by the levitating conductor coils 3, 3' and superconducting coils 1, 1', and the vehicle VH is propelled and guided by the superconducting coils 1, 1' and the conductor coils 2, 2' for propulsion and guidance.
This will be described in greater detail in accordance with FIGS. 2(a) through 4.
As shown in FIG. 2(a), the superconducting coils 1, 1' are arranged vertically at predetermined intervals on both sides of the truck 4 in the direction of travel of the vehicle. The coil-shaped levitating conductor coils 3, 3' are arranged horizontally on the bottom of the track bed 9 and extend continuously with predetermined gaps between them in the direction of travel of the vehicle at positions that allow electromagnetic induction to take place between these coils and the superconducting coils 1, 1'. As long as the vehicle VH is at rest, the magnetic flux produced by the superconducting coils, 1, 1' is not cut by the levitating conductor coils 3, 3'. Accordingly, no current is produced in the levitating conductor coils 3, 3' and, hence, there is no electromagnetic interaction whatsoever between the superconducting coils 1, 1' and levitating conductor coils 3, 3'. The vehicle VH is driven into motion by a linear motor, which is constructed by the superconducting coils 1, 1' mounted on the truck 4 and the conductor coils 2, 2' for propulsion and guidance arranged along the track bed 9. When the vehicle VH runs in this fashion, the superconducting coils 1, 1' travel along the levitating conductor coils 3, 3' disposed at predetermined intervals along the track bed 9 in the direction of vehicle movement, as a result of which a magnetic flux produced by the superconducting coils 1, 1' is cut by the levitating conductor coils 3, 3' so that a current is induced in the latter coils. As shown in FIG. 3, the induced current grows with an increase in the traveling speed of the vehicle VH and saturation occurs at a certain traveling speed of, say, about 200 Km/h. The induced current is held at this level as long as the vehicle runs at this speed or faster. More specifically, the levitating inductor coils 3, 3' shown in FIG. 2(a) develop a linkage flux .phi. of the kind illustrated in FIG. 2(b) drawn to positionally correspond to the coils 3, 3', and a levitating voltage e shown in FIG. 2(c) also drawn to positionally correspond to the coils 3, 3' is induced in these coils so that a current i of the kind shown in FIG. 2(d) flows through them. When the flow of a current ia through the superconducting coils 1, 1' has the direction indicated in FIG. 2(e), the current induced in the levitating conductor coils 3, 3' by the current ia flows in the direction indicated in FIG. 2(e). In consequence, according to Fleming's left-hand law, a levitating force F=B.times.ia is obtained in the superconducting coils 1, 1', where B represents the density of the magnetic flux generated by the levitating conductor coils 3, 3' and ia is the current flowing through the superconducting coils 1, 1' Thus, the vehicle VH is levitated by a repulsive force acting between the currents induced in the superconducting coils 1,1' provided on the truck 4 and in the levitating conductor coils 3, 3' provided on the track bed 9.
The propulsion and guidance of the vehicle VH will now be described.
The cross-sectional areas of the conductor coils 2, 2' for propulsion and guidance are designed to be equal, and the spacing between the superconducting coil 1 and conductor coil 2 and between the superconducting coil 1' and conductor coil 2' are designed to be equal. The conductor coils 2, 2' for propulsion and guidance null-flux connected, as shown in FIG. 4.
As illustrated in FIG. 4, a polyphase propulsion power supply 8 of three or more phases is connected to the conductor coils 2, 2' for propulsion and guidance, as a result of which currents having the same direction, as indicated by the solid arrows in FIG. 4, flow through the conductor coils 2, 2'. Consequently, according to Fleming's left-hand law, an electromagnetic force which drives the superconducting coils 1, 1' in the forward direction is generated between the vertical segments of the conductor coils 2, 2' and the vertical segments of the superconducting coils 1, 1', so that a propulsion force is produced that propels the vehicle VH provided with the superconducting coils 1, 1'.
Assume that the linkage magnetic fluxes developed in the propulsion and guidance conductor coils 2, 2' respectively opposing the superconducting coils 1, 1' are .phi.g, .phi.g' while the vehicle shown in FIG. 1 is running. In such case the relation .phi.g=.phi.g' will hold if the vehicle VH is not displaced in the lateral direction. Accordingly, the linkage magnetic flux developed for a pair of coils will be .phi.g-.phi.g'=0, no current will be induced and, hence, no guiding force will be produced.
On the other hand, if the vehicle VH (FIG. 1) is displaced laterally, the relation .phi.g&gt;.phi.g' (leftward displacement of the vehicle) or .phi.g&lt;.phi.g' (rightward displacement of the vehicle) will hold and the linkage flux developed by the pair of coils will be .phi.g-.phi.g'=.+-..DELTA..phi.g'. As a result, a guiding force proportional to the displacement is produced in a direction which nullifies the displacement. More specifically, as illustrated in FIG. 4, a current having the direction indicated by the dashed arrow flows through the conductor coil 2 for propulsion and guidance owing to the leftward displacement of the superconducting coil 1, as a result of which a repulsive force acts to guide the displaced vehicle to its original state according to Fleming's left-hand law. On the other hand, the superconducting coil 1' is also displaced leftwardly but this displacement causes a current whose direction is indicated by the dashed arrow to flow through the conductor coil 2' for propulsion and guidance. Consequently, the superconducting coil 1' is attracted to the conductor coil 2' according to Fleming's left-hand law.
In this system, powering, coasting, braking and stopping of the vehicle VH are effected by controlling the current that flows into the conductor coils 2, 2' for propulsion and guidance from the propulsion power supply 8.
When the vehicle VH begins to be moved by the propulsion force generated by the conductor coils 2, 2' for propulsion and guidance, levitating force is generated by the superconducting coils 1, 1' and levitating conductor coils 3, 3', and a guiding force is generated by the superconductng coils 1, 1' and conductor coils 2, 2' for propulsion and guidance. After the vehicle VH attains a certain speed, auxiliary wheels 7, 7' (see FIG. 1) are raised and the vehicle is levitated and guided while a constant levitating force is maintained. When the traveling speed of the vehicle VH falls below a certain level, the levitating force diminishes and the auxiliary wheels 7, 7' are lowered to set the vehicle down upon the track bed 9. As shown in FIG. 1, mechanical guidance wheels 5, 5' are rotatably mounted on the ends of respective shafts 6, 6' whose other ends are fixedly secured to the vehicle VH. These wheels 5, 5' are deployed and guide the vehicle VH mechanically while rolling along the side walls of the track bed 9 when the vehicle VH is running on its wheels 7, 7'.
In this magnetic levitating-type railway in which the levitating conductor coils 3, 3' are arranged horizontally on the bottom of the track bed 9 and the superconducting coils 1, 1' are mounted vertically on both sides of the truck 4 opposing the two inner side walls of the track bed 9, it is necessary to pass a large induced current through the levitating conductor coils 3, 3', and there is a limit upon the extent to which power loss ascribable to the levitating conductor coils 3, 3' can be reduced. That is, there is a limit upon how much the traveling resistance of the vehicle VH can be reduced. In addition, since an unstable spring force in the lateral direction is generated by the levitating conductor coils 3, 3', it is required that a stabilizing spring force exceeding the unstable spring force be produced by the conductor coils 2, 2' for propulsion and guidance.
In this connection, an arrangement of the kind shown in FIG. 5 has been proposed for the purpose of reducing electromagnetic traveling resistance in a magnetically levitated railway.
In FIG. 5, elements identical with those shown in FIGS. 1 through 4 are designated by like reference characters. In this proposed arrangement, superconducting coils 10, 10' are attached horizontally to both sides of the truck 4 of vehicle VH and are arranged to be symmetrical about the center of the truck 4. Conductor coils 12, 13 and 12', 13', of identical shape and dimensions, are likewise horizontally attached to surfaces of the track bed 9 that are above and below the superconducting coils 10, 10'. The conductor coils 12, 13 are null-flux connected, as are the conductor coils 12', 13' Thus, the coils 12, 13 and 12', 13' respectively construct conductor coils 11, 11'. These conductor coils 11, 11' are arranged at predetermined intervals continuously along the length of the track bed 9.
In this arrangement, the levitating force is produced by the conductor coils 12, 13 and 12', 13'. If the superconducting coils 10, 10' on the truck 4 are located at positions intermediate the upper and lower conductor coils 12, 13 and 12', 13', respectively, the linkage magnetic flux of the superconducting coils 10, 10' will be zero and the electromagnetic traveling resistance will be zero. When the superconducting coils 10, 10' are displaced upward or downward, a force acts that restores the superconducting coils 10, 10' to their positions midway between the coils 12, 13 and 12', 13'. If the superconducting coils 10, 10' are displaced leftward or rightward, however, an unstable force acts in a direction that increases this displacement. Another problem is that the truck 4 and track bed 9 become more complicated in construction.